Method of adsorbing iodine or bromine

ABSTRACT

The present invention relates to an iodine (I 2 ) or bromine (Br 2 ) adsorbent including a zeolite having a Si/Al ratio of 15 or greater; an I 2  or Br 2  carrier including the I 2  or Br 2  adsorbent; a column filled with the I 2  or Br 2  adsorbent; a article composed of the I 2  or Br 2  adsorbent or having the I 2  or Br 2  adsorbent attached thereto; a method for adsorbing or removing I 2  or Br 2  using the I 2  or Br 2  adsorbent; an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I 2 ) or bromine (Br 2 ) confined in the pores of the zeolite; a semiconductor material including the iodine- or bromine-containing zeolite composite; and a method for preparing an iodine- or bromine-containing product using the iodine- or bromine-containing zeolite composite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/KR2013/010735, filed on 25 Nov. 2013 claiming the priority of KR10-2012-0134078 filed on 23 Nov. 2012, the content of each of which isincorporated by reference herein.

BACKGROUND

1. Field

The present invention relates to an iodine (I₂) or bromine (Br₂)adsorbent including a zeolite having a Si/Al ratio of 15 or greater; anI₂ or Br₂ carrier including the I₂ or Br₂ adsorbent; a column filledwith the I₂ or Br₂ adsorbent; a article composed of the I₂ or Br₂adsorbent or having the I₂ or Br₂ adsorbent attached thereto; a methodfor adsorbing or removing I₂ or Br₂ using the I₂ or Br₂ adsorbent; aniodine- or bromine-containing zeolite composite including a porouszeolite and iodine (I₂) or bromine (Br₂) confined in the pores of thezeolite; a semiconductor material including the iodine- orbromine-containing zeolite composite; and a method for preparing aniodine- or bromine-containing product using the iodine- orbromine-containing zeolite composite.

2. Description of the Related Art

Iodine is a volatile (sublimating), corrosive solid at room temperature.Because of its volatility, it is difficult to accurately weigh theamount of iodine on a scale, and iodine vapor can corrode the scalebeing used. Likewise, bromine, being a highly volatile and corrosiveliquid at room temperature, is difficult to accurately weigh on a scale,and bromine vapor can corrode the scale being used.

Of the 37 known isotopes of iodine, all are radioactive elements exceptthe stable I-127. Whereas most of the radioactive isotopes have veryshort half-lives of 1 day or shorter, I-124, I-125, I-126, and I-131have relatively long half-lives of 4-60 days. Among them, I-131 resultsin the greatest radioactive damage in the event of atomic reactorexplosion. I-129 decays over a very long period of time with a half-lifeof Ser. No. 15/700,000 years. Due to its slow radioactive radiation, itis less dangerous than other radioactive isotopes and is classified as apotential radioactive material since a large amount of radioisotopes,despite slow radioactive radiation, can lead to high radiation doses.However, the capture of this isotope is an important part in the processof nuclear waste because about 0.55% of uranium decays into I-129. SinceI-129 exists naturally at a certain level, it can be used as an indexfor chronometry. That is to say, the trace amount of the naturallyexisting I-129 captured enables accurate timekeeping.

In solutions, iodine usually exists as iodide ions (I⁻) and iodinemolecules (I₂). Theoretically, the iodide anions can be recovered usingan anion exchanger. However, once the ions flow into seawater, it isimpossible to recover the iodide ions using the anion exchanger becauseof the high chloride concentration in seawater. The neutral iodinemolecules are oxidative and are easily converted into iodide ions viaoxidation by various reducing materials present in seawater. Therefore,the neutral iodine molecules need to be recovered from the hydrosphereincluding the sea or air before they are converted into iodide ions. Forthis reason, a method allowing for effective capturing of iodineincluded in water or air may be useful for blocking the propagation ofthe radioactive iodine.

Until recently, activated carbon or zeolite has been used to recoverneutral iodine molecules from water or air. However, these adsorbentstend to reduce a significant amount of the adsorbed neutral iodine toiodide ions. Due to this property, it is difficult to remove iodine,particularly that in water. Therefore, it is necessary to develop aniodine adsorbent or capturing agent capable of capturing neutral iodinewell without converting the neutral iodine molecules to iodide ions.

SUMMARY

Activated carbon (AC) is known to adsorb I₂ well. However, aconsiderable amount of the adsorbed I₂ is reduced to I⁻ by reducingmaterials present in the activated carbon. It is difficult to remove thethus generated I⁻, and the I₂-adsorbing ability of the activated carboncontaining I⁻ is very low. Accordingly, when removing I₂ from waste fuelusing AC filled into a fixed bed, the AC in the fixed bed should bereplaced with fresh AC after several charge-discharge cycles.Accordingly, there is a need for a strong physical adsorbent enablingpurely physical adsorption even after many charge-discharge cycleswithout the need for replacement.

The present inventors have examined various zeolites for theirI₂-adsorbing ability and formation of I⁻ following I₂ adsorption. As aresult, the inventors have found that a zeolite having a high Si/Alratio adsorbs well not only iodine gas (I₂) in the air but also I₂dissolved in water, and the adsorbed I₂ can be separated as I₂ becauseit is not reduced to I⁻. As a result, the zeolite adsorbent can berecycled many times with no decline in adsorbing ability. Also, theinventors have found that the zeolite can adsorb not only I₂ but alsoBr₂ as well. In addition, the inventors have found that the iodine (I₂)confined in the pores of the zeolite can be readily desorbed using anorganic solvent and completely desorbed by heating.

Furthermore, the inventors have found that the iodine- orbromine-containing zeolite composite exhibits semiconductor propertiesand, accordingly, zeolites in which iodine molecules or brominemolecules are included can be used for various applications.

The present invention is based on these findings.

In an aspect, the present invention provides an I₂ or Br₂ adsorbentcontaining a zeolite having a Si/Al ratio of 15 or greater.

Specifically, the zeolite may have a Sanderson partial negative chargeon oxygen (−δ₀) of 0.2 or lower.

Non-limiting examples of the zeolite may include SL-1F, Si-BEA, SL-1,ZSM-5, MTW, silica MTW, silica DDR, high-silica DDR (ZSM-58, Si/Al=190),silica SSZ-73, an all-silica clathrasil DD3R, a silica ferrierite,silica TON, silica LTA, silica ITQ-1, silica ITQ-2, silica ITQ-3, silicaITQ-4, silica ITQ-7, silica ITQ-29, silica ITQ-32, a silica zeolitehaving CHA, STT, ITW or SVR topology, silica FAU, silica AST, a silicazeolite YNU-2 having MSE topology, silica RUB-41, silica ZSM-22, silicaMEL, or a zeolite analogue having a Si/Al ratio of 15 or greater.Preferred examples of the zeolite may include silicalite-1 (SL-1),fluoride (F⁻)-added silicalite-1 (SL-1F) synthesized by adding afluoride (F⁻)-releasing reagent, a beta zeolite having a silica backbone(all-silica beta, Si-BEA), TON having a silica backbone (ZSM-22), aferrierite having a silica backbone (ZSM-35), DDR having a silicabackbone, ZSM-5, etc., or a mixture thereof. In the iodine (I₂) or Br₂adsorbent according to the present invention, the zeolite may be in theform of powder, foam, or film or may be a blended mixture with a naturalpolymer, a synthetic polymer, or another zeolite not having superioriodine- or bromine-adsorbing ability.

In another aspect, the present invention provides an I₂ or Br₂ carrierincluding the I₂ or Br₂ adsorbent according to the present invention; afixed-bed column filled with the I₂ or Br₂ adsorbent according to thepresent invention; and a article composed of the I₂ or Br₂ adsorbentaccording to the present invention or having the I₂ or Br₂ adsorbentattached thereto. The article may be clothing.

Non-limiting examples of methods for preparing a zeolite foam orattaching a zeolite onto a substrate are described in Korean Patent Nos.0392408 and 0607013 owned by the inventors of the present invention,which are incorporated herein by reference.

In another aspect, the present invention provides a method for adsorbingI₂ or Br₂, including adsorbing I₂ or Br₂ using the I₂ or Br₂ adsorbentaccording to the present invention, the fixed-bed column according tothe present invention, or the article according to the presentinvention.

In another aspect, the present invention provides a method for removingI₂ or Br₂, including: adsorbing I₂ or Br₂ using the I₂ or Br₂ adsorbentaccording to the present invention, the fixed-bed column according tothe present invention, or the article according to the presentinvention; desorbing the adsorbed I₂ or Br₂ from the zeolite by bringinginto contact with an organic solvent dissolving I₂ or Br₂, by heating,or by blowing in heated air or nitrogen; and forming an insoluble silveriodide or silver bromide precipitate by reacting the desorbed I₂ or Br₂with AgNO₃.

In another aspect, the present invention provides an iodine- orbromine-containing zeolite composite including a porous zeolite andiodine (I₂) or bromine (Br₂) confined in the pores of the zeolite. Aknown content of iodine or bromine may be captured in the composite.

The iodine- or bromine-containing zeolite composite according to thepresent invention exhibits semiconductor properties and, thus, can beused as a semiconductor material.

In another aspect, the present invention provides a method for preparingan iodine- or bromine-containing product or a compound generated by aniodine or bromine catalyst, including forming an iodine- orbromine-containing product in an organic solvent dissolving I₂ or Br₂via a chemical reaction between iodine or bromine desorbed from theiodine- or bromine-containing zeolite composite according to the presentinvention by the organic solvent and another compound, or forming thecompound in an organic solvent dissolving I₂ or Br₂ via a catalyticaction of the iodine or bromine, desorbed from the iodine- orbromine-containing zeolite composite according to the present inventionby the organic solvent. This is based on the point that the iodine- orbromine-containing zeolite composite confines iodine (I₂) or bromine(Br₂) in pores thereof and the I₂ or Br₂ may be released by an organicsolvent, heat, or contact with hot air or nitrogen.

A zeolite having a Si/Al ratio of 15 or greater can adsorb not onlyiodine (I₂) or bromine (Br₂) gas in the air but also I₂ or Br₂ dissolvedin water. In particular, it can adsorb and capture not only theradioactive iodine gas in the air but also the radioactive I₂ or Br₂dissolved in seawater or underground water. Furthermore, among thezeolites according to the present invention, a zeolite having aSanderson partial charge on oxygen (−δ⁰) of 0.2 or lower convert neitherthe adsorbed I₂ to I⁻ nor the adsorbed Br₂ to Br⁻, and can release I₂ orBr₂ perfectly without loss, by contact with an organic solvent or byheating and, thus, can be recycled indefinitely.

In addition, since the iodine- or bromine-containing zeolite compositeaccording to the present invention, which includes a porous zeolite andiodine (I₂) or bromine (Br₂) confined in the pores of the zeolite,exhibits semiconductor properties, it may be used as a semiconductormaterial. Furthermore, since it captures iodine (I₂) or bromine (Br₂),it may be used for various applications, e.g., as an iodine or brominecarrier or an iodine- or bromine-releasing reagent which releases anexact amount of iodine or bromine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows absorption of I₂ from its saturated aqueous solution ontoactivated carbon (AC) and various zeolites SL-1F, Si-BEA, SL-1, ZSM-5,AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA as solid absorbents.

FIG. 2 shows the absorbed amount (wt %) of iodine (I₂) (the amount (g)of absorbed I₂ per 100 g of zeolite) with time for activated carbon (AC)and various zeolites in aqueous solutions.

FIG. 3 shows sublimation of I₂ from solid I₂, and its absorption intosilicalite foam (SL-1 form) and silicalite powder (SL-1 powder).

FIG. 4 compares the hydrophobicity of activated carbon (AC) and variouszeolites through water vapor adsorption isotherms at 313 K (40° C.).

FIG. 5 shows an apparatus for desorbing I₂ by increasing temperaturewhile injecting nitrogen gas.

FIG. 6 shows the degree of desorption of I₂ from solid absorbentsaccording to temperature.

FIG. 7 shows XRD patterns of MFI-type zeolite powder (freshly calcined),MFI-type zeolite with 0.1%, 1.0%, 6.9%, 22.3%, or 34.4% I₂ adsorbed, andI₂-adsorbed MFI-type zeolite which has been recalcined (recalcination).

FIG. 8a and FIG. 8b respectively show the amount (wt %) of iodide ion(I⁻) formed inside a solid absorbent (8 a) and in a solution (8 b) byactivated carbon (AC) and various zeolites with time. FIG. 8a shows theamount (wt %) of iodide ion (I⁻) formed inside the solid absorbent, FIG.8b shows the amount (wt %) of iodide ion (I⁻) formed in an aqueoussolution, and FIG. 8c shows the total amount of the formed iodide ion(I⁻).

FIG. 9 shows the relationship between the Sanderson partial charge onoxygen and the total amount (wt %) of iodide ion (I⁻) formed inside asolid absorbent and in a solution for activated carbon (AC) and variouszeolites.

FIG. 10A shows the absorbed amount (wt %) of I₂ by activated carbon (AC)and various zeolites from the I₂-saturated aqueous iodide (I⁻) solutionwith various concentrations of I⁻. FIG. 10B shows the absorbed amount(wt %) of I₂ by activated carbon (AC) and various zeolites from theI₂-saturated seawater.

FIG. 11 shows scattering and reflection UV-Vis spectra of Br₂-adsorbedSi-BEA, ZSM-5, and SL-1 DML. It can be seen that the zeoliteseffectively adsorb Br₂.

DETAILED DESCRIPTION

The term zeolite collectively refers to crystalline aluminosilicates.

The zeolite backbone is composed of tetrahedral units formed by [SiO₄]⁴⁻and [AlO₄]⁵⁻, which are bridged by oxygen atoms. Since the Al of[AlO₄]⁵⁻ has a formal charge of +3, whereas the Si of [SiO₄]⁴⁻ has aformal charge of +4, each Al has one negative charge. Accordingly,cations are present for charge balancing. The cations are present not inthe backbone but in the pores and the remaining space is usuallyoccupied by water molecules.

Because the site occupied by aluminum in the aluminosilicate backbone isnegatively charged, there are cations for charge balancing in the poresand the inside of the pores is strongly polarized.

Meanwhile, various analogues (zeotype molecular sieves), wherein thesilicon (Si) and aluminum (Al) constituting the backbone structure ofzeolite have been partially or entirely replaced by various otherelements, are known. For example, a porous silicalite in which aluminumhas been completely eliminated, an (AlPO₄)-type zeolite analogue inwhich silicon has been replaced by phosphorus (P), and other zeoliteanalogues obtained by replacing the backbone metal atoms of a zeolite ora zeolite analogue with various metal elements such as Ti, Mn, Co, Fe,Zn, etc. are known. These analogues are also included in the scope ofzeolite according to the present invention.

Examples of an MFI-type zeolite or an analogue thereof may includeZSM-5, silicalite-1, TS-1, AZ-1, Bor-C, boralite C, encilite, FZ-1,LZ-105, monoclinic H-ZSM-5, mutinaite, NU-4, NU-5, TSZ, TSZ-III, TZ-01,USC-4, USI-108, ZBH, ZKQ-1B, etc. ZSM-5 is an MFI-type zeolite formed ofsilicon and aluminum of a specific ratio, silicalite-1 is a zeoliteconsisting only of silica (SiO₂), and TS-1 is an MFI-type zeolite inwhich titanium (Ti) occupies some of the aluminum sites.

Both SL-1 and SL-1F are MFI-type. SL-1 is synthesized without addingNH₄F at all, whereas SL-1F is synthesized by adding NH₄F tosignificantly increase hydrophobicity.

The chemical composition and the Sanderson partial charge on oxygen ofvarious zeolites are given in Table 1.

TABLE 1 Chemical composition (formula) −δ₀ SL-1 Si₉₆O₁₉₂ 0.1501 Ag-MORH_(4.0)Ag_(1.2)Al_(5.2)Si_(42.8)O₉₆ 0.1596 MORH_(4.0)Na_(1.2)Al_(5.2)Si_(42.8)O₉₆ 0.1613 ZSM-5H_(0.2)Na_(0.75)K_(2.75)Al_(3.7)Si_(94.3)O₁₉₂ 0.1684 CaAH₁₅Ca_(22.5)Na_(34.5)Al_(94.5)Si_(97.5)O₃₈₄ 0.2615 NaYNa_(52.3)Al_(52.3)Si_(139.7)O₃₈₄ 0.2640 NaAH₆Na_(88.5)Al_(94.5)Si_(97.5)O₃₈₄ 0.3251 NaXH₃Na_(92.7)Al_(95.75)Si_(96.25)O₃₈₄ 0.3367

When I⁻ is generated in an I₂ adsorbent, the I₂ adsorbent can no longeradsorb I₂ and the I⁻ is difficult to remove therefrom. When the I⁻exists in a solution, it can be removed using an anion exchange resin ora silver solution. However, when the I⁻ exists inside the adsorbent, itcannot be removed even with the anion exchange resin or silver solution.The inventors of the present invention have examined various zeolitesfor their I₂-adsorbing ability and formation of I⁻ following I₂adsorption. As a result, the inventors have found that there are somezeolites which do not generate or hardly generate I⁻ after I₂adsorption, particularly in water.

A more detailed description is given herein below.

The I₂ concentration of a saturated I₂ aqueous solution is ˜1.5 mM. Itwas investigated whether activated carbon (AC) and various zeolitesZSM-5, SL-1 powder, SL-1 foam, Si-BEA, NaA, NaY, SBA-15, MOR, and AgMORadsorb the I₂ saturated in water well (FIG. 1). As seen from FIG. 1,activated carbon, zeolite ZSM-5, SL-1 powder, SL-1 foam, and Si-BEA canadsorb I₂ in water.

Meanwhile, the adsorption amount (wt %) of iodine (I₂) with time foractivated carbon (AC) and various zeolites SL-1F, Si-BEA (all-silicazeolite-β), SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA wasmeasured in aqueous solutions. As seen from FIG. 2, activated carbon andzeolite SL-1F, BEA, SL-1, and ZSM-5 showed high iodine (I₂) adsorptionamount of 15 wt % or greater, whereas AgMOR, SBA-15, NaY, MOR, NaX, NaA,and CaA hardly adsorbed iodine (I₂).

In addition, the adsorption of I₂ sublimating from solid I₂ wasconfirmed for both silicalite-1 foam (SL form) and silicalite-1 powder(SL powder) which are MFI-type zeolites (FIG. 3). From FIG. 3, it can beseen that the color of the silicalite-1 foam and silicalite-1 powderturns violet due to the adsorption of I₂.

Meanwhile, the hydrophobicity of activated carbon (AC) and variouszeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA,and CaA was investigated through water vapor adsorption isotherms at 313K (40° C.). As seen from FIG. 4, the zeolites SL-1F, Si-BEA, SL-1, andZSM-5 with a larger iodine (I₂) adsorption amount exhibit higherhydrophobicity than other zeolites. That is to say, the iodine (I₂)adsorption amount increases with hydrophobicity, suggesting that theadsorption of iodine (I₂) in the zeolite is due to hydrophobic bonding.The hydrophobicity is in the order of ZSM-5<SL-1<Si-BEA<SL-1F. Since thehydrophobicity of the zeolite increases with the Si/Al ratio, thezeolite according to the present invention capable of adsorbing iodine(I₂) has a Si/Al ratio (molar ratio) of 15 or greater, specifically 20or greater, more specifically 30 or greater. For SL-1, SL-1F, andSi-BEA, which are free from Al, the Si/Al ratio is infinite (∞).

Meanwhile, using an apparatus for desorbing I₂ by increasing temperaturewhile injecting nitrogen gas as shown in FIG. 5, the degree of iodinedesorption depending on temperature was investigated for activatedcarbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 (FIG. 6).Although I₂ is highly volatile, it is not desorbed easily even at hightemperatures once it is adsorbed to the zeolite. As seen from FIG. 6, I₂was desorbed at 175° C. for the zeolites Si-BEA, SL-1F, and SL-1, unlikeactivated carbon (AC). That is to say, I₂ is desorbed from all of theseadsorbents when hot air or hot nitrogen above a certain temperature isinjected. For activated carbon (AC), some of the adsorbed I₂ that turnedto I⁻ remained and iodine was not completely desorbed.

The XRD patterns of SL-1 powder (freshly calcined), SL-1 with 0.1%,1.0%, 6.9%, 22.3% or 34.4% I₂ adsorbed, and I₂-adsorbed SL-1 which hasbeen recalcined (recalcination) were investigated. As seen from FIG. 7,it was observed that the peaks related to porosity disappeared when thenanowire channel in SL-1 was completely filled with I₂ (34.4%). Inaddition, it can be seen from the XRD patterns shown in FIG. 7 that theporosity-related peaks appeared again for the I₂-adsorbed SL-1 which hadbeen recalcined (recalcination), as in the fresh SL-1. This confirmsthat the backbone structure is maintained regardless of the adsorptionand desorption of I₂.

Meanwhile, the amount (wt %) of iodide ion (I⁻) formed inside the solidadsorbent and in a solution with time was measured for activated carbon(AC) and the various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15,NaY, MOR, NaX, NaA, and CaA. The results are shown in FIG. 8a and FIG.8b , respectively. FIG. 8a shows the amount (wt %) of iodide ion (I⁻)formed inside the solid adsorbent, FIG. 8b shows the amount (wt %) ofiodide ion (I⁻) formed in a solution, and FIG. 8c shows the total amountof the formed iodide ion (I⁻).

As seen from FIGS. 8a-8c , the amount of iodide ion (I⁻) formed insidethe solid adsorbent was the highest for activated carbon (AC). Theamount of iodide ion (I⁻) formed in solutions was in the order ofNaX>NaA>CaA>NaY. For MOR, AgM, ZSM-5, SL-1F, SL-1, Si-BEA, and SBA-15,iodide ion (I⁻) was hardly formed either inside the solid adsorbent orin the solution.

FIG. 9 shows the relationship between the Sanderson partial charge onoxygen and the total amount (wt %) of iodide ion (I⁻) formed inside thesolid adsorbent and in the solution for activated carbon (AC) and thevarious zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR,NaX, NaA and CaA.

From FIG. 9, it can be seen that the formation amount (wt %) of iodideion (I⁻) is proportional to the Sanderson partial charge on oxygen foractivated carbon (AC) and the various zeolites. Accordingly, the zeoliteused as an iodine (I₂) adsorbent for preventing iodide ion (I⁻)formation may have a Sanderson partial charge on oxygen (−δ⁰) ofspecifically 0.2 or lower, more specifically 0.1-0.2.

As seen from FIGS. 1-9, the zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 areadvantageous in that they exhibit a high iodine (I₂) adsorption amountand hardly show iodide ion (I⁻) formation inside the solid adsorbent andin the solution. The zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 havestronger hydrophobicity and a lower Sanderson partial charge on oxygenas compared to other zeolites.

Accordingly, the present invention is characterized in that a zeolitehaving a Si/Al ratio of 15 or greater is used as a zeolite for adsorbingiodine (I₂) and, among such zeolites, a zeolite having a Sandersonpartial charge on oxygen (−δ⁰) of 0.2 or lower is used to preventformation of iodide ion (I⁻) from the adsorbed I₂.

FIG. 10A shows the I₂-saturated adsorption amount (wt %) of activatedcarbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 underdifferent I⁻ concentrations. It can be seen that the zeolite accordingto the present invention can adsorb I₂ even when it is dissolved inwater as I⁻.

Additionally, FIG. 10B shows the I₂-saturated adsorption amount (wt %)of activated carbon (AC) and the various zeolites Si-BEA, SL-1F, andSL-1 in artificial seawater (ASW). It can be seen that the zeoliteaccording to the present invention can adsorb I₂ even when it isdissolved in seawater.

I₂ is more soluble in seawater because it forms a complex. The zeoliteaccording to the present invention can readily remove I₂, particularlyradioactive I₂, when it is dissolved in seawater, underground water,etc.

Meanwhile, the zeolites of the present invention can also adsorb Br₂ inwater (FIG. 11).

The zeolite according to the present invention can adsorb I₂ having notonly stable I-127 but also all the isotopes of I described in Table 2.

TABLE 2 Decay Main γ-X-ray energy (keV) Isotope Half-life mode E_(max)(keV) (abundance) ¹²³I 13.27 h EC + β⁺ 1074.9 (97%, EC)  159 (83%) ¹²⁴I4.18 d EC + β⁺ 2557 (25%, EC), 3160 602.7 (63%), 723 (10%), (24%, EC),1535 (12%, β⁺),  1691 (11%) 2138 (11%, β⁺) ¹²⁵I 59.41 d EC 150.6 (100%)35.5 (6.68%), 27.2 (40%),  27.5 (76%) ¹²⁶I 13.11 d EC + β⁺, β⁻ 869.4(32%, β⁻), 1489 (29%, 338.6 (34%), 666.3 (33%) EC), 2155 (23%, EC) ¹²⁷IStable ¹²⁸I 24.99 m β⁻, EC + β⁺ 2119 (80%, β⁻) 442.9 (17%) ¹²⁹I 1.57 ×10⁷ y β⁻ 154.4 (100%) 39.6 (7.5%), 29.5 (20%),  29.8 (38%) ¹³⁰I 12.36 hβ⁻ 587 (47%), 1005 (48%) 536 (99%), 668.5 (96%), 739.5 (82%) ¹³¹I 8.02 dβ⁻ 606 (90%) 364.5 (82%) ¹³²I 2.30 h β⁻ 738 (13%), 1182 (19%), 667.7(99%), 772.6 (76%) 2136 (19%) ^(132m)I 1.39 h IT, β⁻ 1483 (8.6%, β⁻) 600(14%), 173.7 (8.8%) ¹³³I 20.8 h β⁻ 1240 (83%) 529.9 (87%) ¹³⁴I 52.5 m β⁻1307 (30%) 847 (95%), 884 (65%) ¹³⁵I 6.57 h β⁻ 970 (22%), 1388 (24%) 1260 (29%) Half-lives of the isotopes are given as m: minutes; h:hours; d: days; and y: years. The decay mode: EC for electron capture;β⁺ for positron emission; β⁻ for beta emission; IT for internaltransfer. An isotope may decay by more than one mode.

Meanwhile, the solubility (wt %) of iodine (I₂) of SL-1F and BEA wascompared in various organic solvents. The results are shown in Table 3.Electron donor solvents can dissolve a large amount of I₂ because theyform electron donor-acceptor complexes. Even though silicalite-1 (SL-1F)is a weak electron donor, the solvent can dissolve a very large amountof I₂.

TABLE 3 Solubility of I₂ at Solvent density Solvent weight ConcentrationSolvent 25° C. (g/100 mL) (g/mL) (g) (%) wt % Ethanol 21.43 0.79 79.021.34 27.12 Diethyl ether 25.20 0.71 71.0 26.19 35.49 AcOH 14.09 1.05105.0 11.83 13.42 Benzene 14.09 0.88 88.0 13.80 16.01 CHCl₃ 14.09 1.48148.3 8.68 9.50 CCl₄ 2.603^(a) 1.59 159.0 1.61 1.64 Carbon disulfide(CS₂) 16.47 1.26 126.0 11.56 13.07 Water 0.029^(b), 1.00 100.0 0.029,0.029, 0.078^(c) 0.078 0.078 Hexane (exp. 0.94 0.66 65.9 1.41 1.43 data)Silicalite-1 63.72 1.80 180.0(100 mL) 26.14 35.40 (SL-1F) BEA 56.96 1.61161.0(100 mL) 26.25 35.60 AC 11.55 0.32  32.0(100 mL) 26.52 36.10 ^(a)at35° C., ^(b)at 20° C., ^(c)at 50° C., density of I₂ = 4.93 g/mL.

As can be seen from Table 3, although the I₂ adsorbed to the zeoliteaccording to the present invention cannot be removed in water, it can beremoved using organic solvents exhibiting high solubility for I₂.However, the I₂ adsorbed to activated carbon (AC) cannot be removed evenwhen organic solvents exhibiting high solubility for I₂ are used. Sincethe zeolite according to the present invention is hydrophobic, it has astrong tendency to absorb the organic solvent and the absorbed organicsolvent dissolves I₂, thereby releasing I₂ from the zeolite.

The zeolite according to the present invention can be recycledindefinitely since the I₂ adsorbed thereto can be completely removedusing organic solvents such as ethanol. In contrast, activated carbon(AC) must be discarded after 3-4 uses because the I₂ adsorbed theretocannot be removed by water or organic solvents. Accordingly, whereas thezeolite according to the present invention can be used indefinitely whenfilled into a fixed-bed column since I₂ adsorbed thereto can becompletely removed using organic solvents, the activated carbon (AC)being filled into a fixed-bed column as an I₂ adsorbent requires routinereplacement.

Non-limiting examples of the organic solvent for dissolving I₂ from thezeolite may include ethanol, diethyl ether, AcOH, benzene, CHCl₃, carbondisulfide or a mixture thereof.

Meanwhile, the I₂ recovered from the zeolite and remaining dissolved inthe organic solvent may be converted to small-sized AgI or AgIOprecipitates by reacting with a AgNO₃ aqueous solution for permanentburial.

The inventors of the present invention found that an iodine- orbromine-containing zeolite composite including a porous zeolite andiodine (I₂) or bromine (Br₂) confined in the pores of the zeoliteexhibits semiconductor properties with a narrow band gap energy (E_(g)).For example, it may have a band gap energy E_(g)<3.0 eV and anelectrical conductivity of 0.1 siemens/m or greater.

Specifically, a result of measuring the electrical conductivity ofiodine-containing silicalite-1 (I₂@SL-1) by electron force microscopywas as follows:σ_(a) along a-axis=1.67×10⁴Sm⁻¹σ_(b) along b-axis=1.99×10⁴Sm⁻¹

In addition, since the iodine (I₂) captured in the iodine-containingzeolite composite according to the present invention is not evaporatedat temperatures of 50° C. or lower, it allows accurate quantification ofiodine. It can be applied for a variety of chemical reactions requiringiodine because an accurate known amount of iodine is released by anorganic solvent if the iodine-containing zeolite composite which hasbeen quantitated is added to a reactor.

Additionally, the iodine-containing zeolite composite according to thepresent invention may be used as a controlled-release system by slowlyadding a solvent that enables release of iodine.

This application also holds true for the bromine-containing zeolitecomposite.

What is claimed is:
 1. A method of adsorbing I₂ or Br₂ and convertingneither the adsorbed I₂ to I⁻ nor the adsorbed Br₂ to Br⁻, comprisingadsorbing I₂ or Br₂ on a I₂ or Br₂ adsorbent containing a zeolite havinga Si/Al ratio of 15 or greater and a Sanderson partial negative chargeon oxygen (−δº) of 0.2 or lower, wherein the zeolite is selected fromthe group consisting of SL-1F, Si-BEA and SL-1.
 2. The method of claim1, wherein the adsorbed iodine (I₂) comprises radioactive iodine.
 3. Amethod of removing I₂ or Br₂, comprising: adsorbing I₂ or Br₂ withoutconverting the adsorbed I₂ to I⁻ or the adsorbed Br₂ to Br⁻, on a I₂ orBr₂ adsorbent containing a zeolite having a Si/Al ratio of 15 or greaterand a Sanderson partial negative charge on oxygen (−δº) of 0.2 or lower,wherein the zeolite is selected from the group consisting of SL-1F,Si-BEA and SL-1; desorbing the adsorbed I₂ or Br₂ from the zeolite bycontacting the I₂ or Br₂ adsorbent with an organic solvent dissolving I₂or Br₂, by heating the I₂ or Br₂ adsorbent, or by blowing the I₂ or Br₂adsorbent in heated air or heated nitrogen; and forming a precipitate byreacting the desorbed I₂ or Br₂ with AgNO₃.
 4. The method for removingI₂ or Br₂ according to claim 3, wherein the organic solvent is ethanol,diethyl ether, AcOH, benzene, CHCl₃, carbon disulfide, or a mixturethereof.